1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus and, in particular, to an improved tray transfer unit and an automatic test handler including such a tray transfer unit.
2. Description of the Related Art
After being sawed from a wafer, semiconductor devices are typically placed in trays during certain points during their manufacture to reduce the likelihood of damage and to increase the ease with which the semiconductor devices may be handled. The semiconductor devices are typically removed from a tray for processing and discharged to the same or a different tray after processing in a manner that maintains the order in which they are arranged in the original tray. The semiconductor devices are also typically transferred between processing equipment as they are arranged in a tray.
The semiconductor devices are typically transferred between processing equipment by an operator, and are then transferred within the processing equipment using a tray transfer unit. The tray transfer unit is installed in a loading part or an unloading part of the processing equipment to load or unload the trays containing the semiconductor devices. The tray transfer unit may be incorporated in an automatic test handler used in a test process so that trays containing the semiconductor devices to be tested can be loaded and those devices that have been tested can be unloaded automatically. A conventional automatic test handler with a tray transfer unit is described below.
FIG. 1 is a plan view of a conventional automatic test handler. FIG. 2 is a front view of the conventional automatic test handler. As illustrated in FIGS. 1 and 2, the conventional automatic test handler 300 comprises a tester (not shown) for testing the semiconductor devices, a first chamber 353 for establishing the temperature condition for test typically by heating or cooling the semiconductor devices to one or more temperatures as much as 50° C. or more above or below room temperature, a second chamber 355 for restoring the tested semiconductor devices to a temperature much closer to room temperature and a pick and place device 370 for transferring the semiconductor devices. The conventional automatic test handler 300 further comprises a plurality of tray stockers 311 having supply trays 21 and receiving trays 22, a tray transfer unit 320 for transferring the supply tray 21, grippers 341 for supporting the supply trays 21 and a control unit 380 for controlling the overall operation.
The loaded supply trays 21 containing a number of semiconductor devices are loaded in the tray stocker 311. A supply tray 21 is then transferred to the gripper 341 by the tray transfer unit 320. The semiconductor devices in the supply tray 21 may then be temporarily placed in a buffer 385 and finally placed onto a test tray 31 provided on a conveyor belt 357 by the pick and place device 370. The test tray 31 is moved into the first chamber 353 to establish the test temperature(s) for the semiconductor devices in the test tray 31. The test tray 31 is then transferred to the tester in which semiconductor devices in the test tray 31 are determined to pass or fail predetermined functional and/or parametric test processes.
After the test process is completed, the test tray 31 having the tested semiconductor devices is transferred to the second chamber 355 where the tested semiconductor devices are typically restored to a normal temperature of about 25° C. The semiconductor devices are then transferred by the pick and place device 370 through the buffer 385 and returned to open pockets on a supply tray 21 or a receiving tray 22 supported by a gripper 341 and may be sorted according to the test results. The trays, once loaded with tested and sorted semiconductor devices, are then transferred to the tray stocker 311 for unloading.
The conventional automatic test handler may automatically load or unload the semiconductor devices, thereby reducing the test time and eliminating the need for additional operator involvement, which may lead to increased productivity. The conventional automatic test handler, however, has disadvantages. For example, a so-called double device fault may occur during the test process. A double device fault refers to a fault where two or more semiconductor devices are placed in a single pocket or receptacle of the tray. A double device fault may result from the malfunction of an adsorption component, e.g., a vacuum adsorptive pad or a vacuum pump, or from the malfunction of a component used to detect the adsorption of the semiconductor device, e.g., a sensor.
If such a fault is caused by the malfunction of a component related to vacuum, it may be that a vacuum adsorptive force was not properly applied through the vacuum adsorptive pad or was improperly released. In such instances, the semiconductor device may not be adsorbed for loading or unloading, or may be released prematurely during transfer.
If the fault is caused by the malfunction of a component used to detect the adsorption, the adsorption of the semiconductor device by the vacuum adsorptive pad may not be detected accurately and may generate erroneous loading data. Errors in loading data may be transmitted to the control unit of the automatic test handler. As a result of the erroneous data, the control unit may attempt to load another semiconductor device in a pocket already containing a semiconductor device that has not been properly recognized or acknowledged by the control unit.
In order to prevent a double device fault, the components related to vacuum adsorption or detection of adsorption should be replaced or repaired before the durability of the components is exceeded either as a result of forced or natural deterioration or through faults generated by other causes. However, the durability of the components is affected by the environment, rendering it difficult to measure or estimate the durability of the component with sufficient accuracy to ensure that corrective maintenance is performed in a timely manner. Further, if faults are the result of causes other than exceeding component durability, the repair or replacement of such components may not be required.
For the above reasons, it has proven difficult to eliminate double device faults completely thereby making it necessary to detect a double device fault when it occurs so that corrective action may be taken.